The expression of the albumin gene is a characteristic function of the normal liver, where this protein is the major product of the protein synthetic apparatus. Albumin is also synthesized by certain stable rat hepatomas, but in reduced amounts or with translational alterations. In this investigation, the molecular modifications in the post- transcriptional regulation of the albumin gene in albumin-synthesizing tumors will be examined and compared with the corresponding elements of the normal rat liver. Albumin-synthesizing polyribosomes will be isolated by specific immunoprecipitation, from which the mRNA will be purified, characterized, and used for the synthesis of a complementary DNA. These tools will then be used to quantitate cytoplasmic mRNA levels and distribution, identify albumin mRNA-specific protein synthesis initiation factors, characterize the mRNA and its associated proteins, and to search for a nuclear precursor to the polysomal mRNA. The ability to isolate and characterize the components involved in the altered post-transcriptional expression of a single gene product should lead to a rational approach to the study of control processes in neoplasia.